Ancillary confirmatory tests

General

Ancillary investigations are NOT required for the diagnosis and confirmation of death using neurological criteria.

Useful when brainstem testing is not possible

Extensive facio- maxillary injuries
Residual sedation
Some cases of paediatric hypoxic brain injury
Where a primary metabolic or pharmacological derangement cannot be ruled out or in cases of high cervical cord injury,
Where spontaneous or reflex movements in the patient generate uncertainty over the diagnosis.

Ancillary confirmatory test

May reduce any element of uncertainty
Foreshorten any period of observation prior to formal testing of brain-stem reflexes.

Any ancillary or confirmatory investigation should be considered ADDITIONAL to the fullest clinical testing and examination (as outlined above) carried out to the best of the two doctors capabilities in the given circumstances.

Types of test

Clinical

Doll eye response

Rotation of the head to either side should not produce any eye movement (absent doll’s eyes response).
This should NOT be performed if there is suspected or known cervical spine injury.

Administration of 2mg atropine

Should not lead to an increased heart rate (more than 3%).

Neurophysiological test

Loss of bioelectrical activity in the brain (EEG, evoked potentials).

Criteria: Definition of electrocerebral silence on EEG

No electrical activity > 2 mcV with the following requirements

Recording from scalp or referential electrode pairs ≥ 10cm apart

8 scalp electrodes and ear lobe reference electrodes

Inter-electrode resistance < 10,000 Ω (or impedance< 6,000 Ω) but over 100 Ω

Sensitivity of 2 mcV/mm

Time constants 0.3–0.4 sec for part of recording

No response to stimuli (pain, noise, light)

Record> 30mins

Repeat EEG in doubtful cases

Qualified technologist and electroencephalographer with ICU EEG experience

Telephone transmission not permissible

Pros

Can be done at bedside.

Cons

Requires experienced interpreter.
Does not detect brainstem activity, and electrocerebral silence (ECS) (i.e., isoelectric EEG) does not exclude the possibility of reversible coma.

Use ECS as a clinical confirmatory test only in patients without drug intoxication, hypothermia, or shock, and not in patients where brainstem activity might be preserved (i.e. situations where the clinical brainstem exam cannot be performed).
Note: a practical problem with EEG for brain-death determination is that it is often difficult to get a tracing that is totally free of electrical signal, even in patients who are brain dead by other criteria.

Auditory Evoked potentials

In using auditory evoked potentials in the evaluation of brain death, what wave is necessary for the test to be valid?

Wave I, at least on one side

SSEPs

Findings

Bilateral absence of N20-P22 response with median nerve stimulation OR
Disappearance of the P14 peak at medial lemniscus and nucleus cuneatus on nasopharyngeal electrode recordings.

Studies were judged as Class III data, and that while P14 recordings could be a valuable confirmatory test,
No interobserver variability studied.

Radiological test

Absent cerebral blood flow or brain tissue perfusion

Cerebral angiography

Evidence

Absence of cerebral blood flow, which is incompatible with brain survival.

Pros

Highly sensitive for determining death of cerebral hemispheres.

Cons

Costly
Time-consuming,
Requires transport of the patient to X-ray department
Invasive,
Potentially damaging to organs that may be used for donation,
Not optimal for detecting small amount of blood flow to brainstem.
Requires a radiologist and technician.

Criteria

Absence of intracranial flow at the level of the carotid bifurcation or circle of Willis.

Filling of the superior sagittal sinus may occur in a delayed fashion and is not incompatible with brain death.
Interobserver validity has not been studied.
Not routinely used in the diagnosis of brain death, but may be employed in difficult situations.

Cerebral radionuclide angiogram (CRAG)

Can be done using a gamma camera, or more contemporary HMPAO SPECT (for 99mTechnetium hexamethylpropyleneamine oxime single-photon emission CT).
May not detect minimal blood flow to the brain, especially brainstem.
Cons

Necessitates transport to the radiology/nuclear medicine department
Requires an experienced interpreter.

May be useful to confirm clinical brain death in the following settings

Where complicating conditions are present, e.g. hypothermia, hypotension (shock), drug intoxication… (e.g. patients emerging from barbiturate coma), metabolic abnormalities
In patients with severe facial trauma where evaluation of ocular findings may be difficult or confusing
In patients with severe COPD or CHF where apnea testing may not be valid
To shorten the observation period

Technique

Using gallium camera

Scintillation camera is positioned for an AP head and neck view

Inject 20–30 mCi of 99mTc-labeled serum albumin or pertechnetate in a volume of 0.5–1.5 ml into a proximal IV port, or a central line, followed by a 30ml NS flush
Perform serial dynamic images at 2 second intervals for ≈ 60 seconds
Obtain static images with 400,000 counts in AP and then lateral views at 5, 15 & 30minutes after injection
If a study needs to be repeated because of a previous non-diagnostic study or a previous exam incompatible with brain death, a period of 12 hours should lapse to allow the isotope to clear from the circulation

Criteria

Findings No uptake in brain parenchyma= “hollow skull phenomenon”
Termination of carotid circulation at the skull base, AND
Lack of uptake in the ACA and MCA distributions (absent “candelabra effect”).
There may be delayed or faint visualization of dural venous sinuses even with brain death, due to connections between the extracranial circulation and the venous system.

MRI and MR angiography (MRA)

MRA is very sensitive for detecting loss of blood flow in cavernous ICA;
Specificity has not been accurately evaluated3 (i.e., might give false positives for brain death in comatose patients)
Not considered a valid confirmatory test.

CT angiography (CTA)

Blood flow on CTA (i.e., not consistent with brain death) was seen in patients with isoelectric EEG. False positive rate had not been determined in comatose non-brain dead patients. CTA is not considered to be a valid confirmatory test for brain death.3

Transcranial Doppler

Not widely used.
Small peaks in early systole without diastolic flow or reverberating flow (indicative of significantly increased ICP)
Initial absence of Doppler signals cannot be used as criteria for brain death since 10% of patients do not have temporal insonation windows

Less reliable